1. Field of the Invention
The present invention relates to a fiber reinforced cement composition using a hydraulic inorganic material such as cement, products thereof and a manufacturing process thereof.
2. Description of the Related Art
The following description sets forth the inventor's knowledge of related art and problems therein and should not be construed as an admission of knowledge in the prior art.
Hitherto, Asbestos has been used as reinforcement of fiber reinforced cement products. Recently, however, woody reinforcements such as wood flakes and wood fibers and organic synthesis fibers have come to be used instead of conventional asbestos since environmental pollution (such as pneumoconiosis) caused by flying of fine powder of asbestos has become a serious problem.
Even more particularly, in late years, as for the crystalline silica such as quartz, tridymite, cristobalite, it is said to asbestos similar that harmful effect may be given to human body in siliceous.
Therefore administrative level/allowable concentration of crystalline silica as dust is established in ACGIH (American Conference of Governmental Industrial Hygienists) and OSHA (Occupational Safety & Health Administration).
For example, allowable concentration of aspiration of crystalline silica-related dust is established in ACGIH as follows:
Quartz is no more than 0.05 mg/m3,
Cristobalite is no more than 0.05 mg/m3,
Tridymite is no more than 0.05 mg/m3.
On the other hand, allowable concentration of aspiration characteristics dust of water-insoluble or the poor solubility material which cannot be classified elsewhere except crystalline silica is lower than 3 mg/m3, and allowable concentration of aspiration characteristics dust of crystalline silica is much severer.
In addition, in Japan, Nihon Sangyo health society assumes that a crystalline silica can be judged by enough evidence from an epidemiologic study for human if cancer-causing based on announced sorting of International Agency for Research on Cancer, and it is established in the first subgroup same as asbestos.
The description herein of advantages and disadvantages of various features, embodiments, methods, and apparatus disclosed in other publications is in no way intended to limit the present invention.
For example, certain features of the preferred embodiments of the invention may be capable of overcoming certain disadvantages and/or providing certain advantages, such as, e.g., disadvantages and/or advantages discussed herein, while retaining some or all of the features, embodiments, methods, and apparatus disclosed therein.